Oh, while I'm thinking about it...
A little while ago, I made a very basic
autohotkey script that simulates holding down the left mouse button when I click my fourth mouse button. I don't know how I managed to mine before I had it. And it's only cheating if you believe the authentic Minecraft experience includes wearing your index finger down to the bone. It doesn't make you mine any faster or anything like that.
In any case, here's a standalone version of the script in case you're interested:
http://zedpower.dreamhosters.com/misc/MiningBuddy.exeIt should work even without autohotkey installed. Run it, then hit your 4th mouse button, and you will swing continuously; simply left-click once to stop swinging. The program puts a white-H-on-green-square icon in your system tray, which you can right-click to shut it down once you're done.
I could make it work with other keys or buttons instead of mouse4 but at that point you'd probably be better off getting autohotkey yourself, it's really not a difficult program to work with, plus it's free and open-source and all that hippie crap. (If you do have or get autohotkey, the script is this single line:
XButton1::Send {Click down}. Change
XButton1 to whatever. Clicking the left mouse button for real sends the
Click up event, so that's really all you need.)
Oh, and, uh, this is only for Windows. And I didn't put a virus in there but who knows, it's the Internet amirite guys? Software provided as is, no warranties, it probably won't make your computer explode but if it does I wash my hands of it, and that'll be my defense in court moments before they put me in the chair.